656 Bates Medal-ruling Machine. ["Jul?, 



are many strong points of internal evidence which would bear me out 

 in asserting that the instrument now before me has been made a long 

 time — has been patched up for experimental trials by its maker — has 

 been thrown aside in favor of his new invention, and has been now 

 been finally brushed up for exportation to India ! 



After bringing so serious a charge forward, it becomes my duty to 

 support it with proof: — and this I can do from Mr. Bate's own written 

 instructions, which bid me " where the coin is in high relief, to lessen 

 the angle of axis B. to diminish the effects of distortion ;" whereas in 

 the following description of his patent, he prides himself on his son's 

 having obviated all distortion*. He begins with a description of the 

 original or American instrument illustrated by a diagram, which I have 

 introduced as fig. 1 . into the accompanying Plate XXIX. 



" a, being the medal; b, the copper plate covered with an etching-ground; 

 C, the tracer; and d, the etching-point at right angles to it. 



" The arm c d having a ruling motion horizontally across the surfaces of a and 

 b, and likewise moving freely in the direction c d. Also vertical motion being 

 given to a and horizontal to b by the same screw : a series of lines traced over 

 the medal were described upon the plate in the following manner: so long as 

 the tracer moved over the plane surface or ground of the medal, the point d de- 

 scribed equidistant straight lines upon the plate ; but so soon as the tracer 

 touched a part of the raised surface or relief of the medal, it was raised above 

 its plane a quantity equal to the height of such relief, and the line described 

 by the etching-point was no longer equidistant, but deviated an equal quantity 

 upon the horizontal plater in the succeeding line, the tracer being raised off 

 still further by the increased height of the relief, the etching-point deviated still 

 further from the former line described upon the plate: the continuation of this 

 process produced a succession of deviating lines upon the plate, which opening 

 as the tracer rose above the plane of the medal, and closing again as it approach- 

 ed that plane gave the effect of light and shade in the printed impression of the 

 plate. But however pleasing the effect of these impressions, they were all 

 distorted representations of the original, just so much as the lines producing the 

 representation deviated from the straight line upon the medal — and I found that 

 this distortion had suspended the use of the process which had been described 

 14 years before in the Manuel de Tonrneur. The most valuable subjects, those 

 having the highest relief, being most distorted." 



Here let me pause — the defects above condemned, are possessed in 



the fullest degree by the ruler sent to me : — the tracer describes 



straight lines only across the medal, while the diamond engraving? point 



traces curves deviating in proportion to the relief of each part : — so 



that if the relief of the central point of the medal be one-tenth of an 



inch raised, and the angle of axis b be fixed at 45°-j- , the same point will be 



ranted not to break! — the bulbs were so thick that when heated even to 300° 

 Farh., there was no chance of the mercury making its appearance in the tube J 

 It was doubtless calculated by the makers that they would never even be tried, 

 much less used! 



* See Philosophical Magazine 1833, vol. 2, page 288. 



f Without a drawing of the instrument it is almost impossible to explain 

 what is meant by axis A and axis B. The first is the axis upon which the rod 

 holding the tracing point turns in rising over the raised parts of the medal, and 



